A systematic calculational procedure is developed for the design of micellar-enhanced ultrafilters to treat aqueous streams contaminated with organic pollutants. Flat plate, spiral wound, hollow fiber, and tubular modules are evaluated for performance (reduction in organic concentration and volume reduction of the retentate) and cost (capital and operating). Membranes having a 5000 molecular weight cutoff (MWCO), which reject all micelles, and 50 000 MWCO membranes, which do not, are used as examples. The surfactant considered is hexadecyl(=cetyl)pyridinium chloride (CPC), and the organic pollutants are chlorobenzene, trichloroethylene, tetrachloroet-hylene, and toluene. The goal is to design an ultrafiltration system to reduce the concentration of a pollutant from its saturation value in water to the Environmental Protection Agency pretreatment standard for municipal sewage. A combined osmotic-pressure and fouling-resistance model quantifies the ultrafiltration permeate flux. Also important are the molar solubilization ratios of the respective organics in aqueous CPC solutions, the osmotic pressure of the surfactant as a function of concentration, and the intrinsic rejection behavior of the membranes for surfactant monomers and micelles. An equilibrium-staged configuration operating countercurrently is proposed for the ultrafiltration system. For treatment of 7.6 m(3) per day [2000 gal/day] of wastewater saturated with chlorobenzene, the optimal design consists of a 3 equilibrium stage system using 18 tubular 50 000 MWCO modules in the first stage operating at 207 kPa [30 psig], 2 spiral wound 50 000 MWCO modules in the second stage operating at 207 kPa [30 psig], and 2 spiral wound 5000 MWCO modules operating at 1034 kPa [150 psig] in the final stage. The optimum volume concentration ratio is 6; the surfactant concentrate leaves the ultrafilter at 17 kg/m(3), and the crossflow velocity is 2 m/s in each stage. This design eliminates the need for prefiltration of the total feed and minimizes capital and operating costs.